Typically, no two people perform the same activity in the same way. That is, while each person may want the same end result for an activity, their methods for achieving the end result will vary due to differences in physical abilities and/or mental abilities. For example, one chef might only need a list of ingredients to prepare a particular meal while another chef might need the ingredients lists, the order of preparation, time for mixing/cooking, etc. in order to prepare the same meal. Another example of this situation is golf. No two golfers are built the same way so no two golfers will have the same golf swing. Accordingly, teaching golf professionals will generally tailor their instruction for a particular individual. For the golfer to truly benefit from such specialized golf instruction, the golfer must practice what he was taught on his own. However, without the teaching professional at the golfer's side, it can be very difficult to remember all of the instruction tips one receives during a golf lesson.
In addition to the fact that different people apply different methods to achieve the same end result, many activities (e.g., jobs, hobbies, sports, etc.) require the use of one's hands in the activity. This can make it difficult for one to consult notes about how the activity should be performed. Once again, consider the case of a golfer whose hand placement and movement are critical to the end result. That is, it would not be desirable or practical for a golfer to consult hand-held notes about his specialized golf instruction while he was trying to practice.